Electrolytic cell with welded anode assembly



April 24, 1951 A. F. BENNING ET AL ELECTROLYTIC CELL WITH wELDED ANonjE ASSEMBLY Filed July 17, 1945 5 6 /0 9 L N1 Hg 7: L* 1 1 in;

@2M MM Patented Apr. 24, 1951 ELECTROLYTIC 'CELL WITH WELDED ANODE ASSEMBLY Anthony F. Benning and Robert C. McHarness, Woodstown, N. J., 'and Melbourne K. Richards and George W. Feldmann, Wilmington, Del., assignors to the United States of America as represented by the United States Atomic Energy Commission Application July 17, 1945, Serial No. 605,544

1 Claim. 1

This invention r-elates to electrolytic cells for the manufacture of iluorine by the electrolysis oi fused salt electrolytes comprising an alkali-metal fluoride and hydrogen fluoride. The invention is `especially concerned with the' provision of a more durable anode supporting structure than hitherto developed.

In the manufacture of elemental iluorine by electrolysis of acid alkali-metal iiuorides serious corrosion problems are involved. These problems result from the corrosiveaction o constituents of the electrolyte and the generated fluorine, They are aggravated by attempts to operate cells at high production rates and consequently at high `current densities. l

At high production rates the removal of heat from the electrolytic cellbecornes a substantial problem. Heat removal can be accelerated by providing electrodes which are wholly immersed so that the electrolyte can circulate freely around the electrodes. With such an arrangement the cooling of the electrolyte at the cell walls increases the density of the electrolyte between each electrode and the adjacent cell wall as compared with the density of the electrolyte between the two electrodes,l and circulation of the electrolyte takes place on the thermo-siphon principle. The generation of gaseous electrolytic products between the electrodes further reduces the relative densities of the liquid and accelerates this circulation.

At high current densities in particular, cell parts which are in contact with the electrolyte .andwhich are electrically -anodic are `relatively7 ViiuorideV protective coating, which normally proa diaphragm potential intermediate the anode and cathode potentials and varying in accordance with the relative position of the diaphragm. Since the potential drop between liquid and anode is greater than the potential drop between liquid and cathode, a diaphragm located at a position equidistant from the two electrodes will have -a potential closer to the cathode potential.

the container, the container may be maintainedY at substantially the diaphragm potential pro'- vided that the container and diaphragm are adequately insulated from the anode and cathode. While this expedient is effective for reducing corrosion of the metal container, it is ob-viously incapable of use for controlling corrosion of the anode support` l During electrolysis the nickel anode is gradually destroyed and eventual replacement is necessary. However with previous anode supports, the corrosion of the anode has not proceeded uniformly at all areas and one of the areas of major weakness has been the margin along the anode support. The metals composing the anode support itself have also' deteriorated rapidly at high current densities. This rapid destruction of the anode assembly by the corrosive compounds of the electrolyte might be avoided to a substantial extent by extending the nickel anode above the surface of the electrolyte and locating the con-- nection of anode to its support entirely in the gas space of the anode chamber. However, such a construction would seriously interfere with the free circulation of electrolyte with consequent increased corrosion of the anode due to temperature variations. Moreover, the adverse effects of inadequate electrolyte circulation are reflected in reduced efliciency of operation as well as increased corrosion. Consequently such a structure does not provide a satisfactory solution for the problem.

l An object of the invention is to provide an electrolytic cell capable of operation for the production of luorine at high current densities and high eiciencies with a minimum of corrosion to cell parts. A further object of the invention is to provide an anode supporting structure which will resist the corrosive effect of luorine and hydrogen fluoride and other electrolyte components and will not only outlast the anode but will not contribute to the rapid corrosion of the anode along the margins of support. Further objects will become apparent from the following description of the invention.

' In accordance with the present invention a nickel anode which terminates below the normal electrolyte level is supported by supporting means comprising a portion composed of a metal having an atomic number from 26 to 29, inclusive, or an alloy thereof, welded to the nickel anodeby a weld, or welds, located in rear of the anode so that it is out of the zone of active electrolysis and is shielded by the anode from the highly 3 corrosive environment b-etween the anode and cathode.

With the supporting structure disposed behind the anode, the anode face opposed to the cathode presents a smoothsurface free fromridges or depressions which would serveV to hold elemental fluorine and form pockets of corrosion.

The anode support preferably comprises a rela-Y tively massive bar of such a metal' andA an ele-- ment or section extending above the normal e'lectrolyte level and presenting to the electrolyte in the zone above the nickel anode; a, copper 01" cupronickel alloy surface, which is particularly resistant to the corrosive actionof, the environment. Preferably the nickelA anode is'welded substantially completely across its face to both adjacent edges of the bar. These welds may be continuous or intermittent but should attach a-major proportion of the length of each bar at bothedges. Continuous welds have the advantage of providing the least resistancetov current between thebar andthe anode. However any irregularity in rate of nickel consumption caused by voltage drop through the supporting bar can be oifset by interrupting the weld bead at the location where` excessive current flows, to provide a slightly higher potentialv difference between the anode and the support. Normally a sufciently large supporting bar is used' to avoid materialvoltage drop throughthe support so that further equalizing measures 4are not necessary.

Ina preierred formof the invention asteelbar is located in rear of the anode in a substantially horizontal position. toa copper supportA and connector by a weld or by means of steel bolts.v The bar may be disposed at the topor bottom ofi the nickel anode or at an intermediate position. In this construction the life of the connector bar is` promoted by its locationin a shielded zone and by the coherent film of ferrie fluoride which forms on the metal surface and renders it. relatively insensitive tothe action of the corrosive agentspresentin the electrolyte.

Cells constructed in accordance with the teachings of the invention havebeen found capable of operating for many hundreds of hours without deterioration of the electrical connection or loss of rigidity of thev physical support for the nickel anode. By use of these connectors it has been possible to avoidv connector corrosion problems and to operate cells for the full life of the anode (several hundred thousand ampere hours in a cell with about 'l1/2 square feet of anode area) at high anodic current densities (150-250 amperes per square foot).

The invention is illustrated by thespecic embodiments shown in the accompanying drawing wherein Figure 1 is a vertical elevation with one end cut Vaway to show diagrammatically the interior arrangement of an electrolytic cell embodying a preferred form of the invention;

Figure 2 is a perspective View of the anode assembly of the cell shown in Figure 1;

Figures 3 and 4 are vertical elevations showing the back and end, respectively, of an alternative anode assembly embodying the invention.

With especial reference to Figurey l, theA numeral I designates the steel container of an electrolytic. cell having a heatingv and cooling jacket Z and provided withr an inlet 3 for electrolyte, a drain outlet 4, and gas outlets 5 and 6, for hydrogen and fluorine, respectively. A Monel barrier l'divdes the, gas space above the electrolyte into The bar in turn is aiiixedv 552 found to be more effectivethan iron, cobalt, or

two chambers for collecting fluorine produced at the anode and hydrogen produced at the cathode, and also supports a perforated Monel partition or diaphragm 8 for inhibiting intermingling of ,iluorineand hydrogen. Depending fromV the top of the electrolytic cell and suitably insulated therefrom are duplicate copper connectors 9 and 9", which connect to the positive pole of a suitable source of electricl current and connectors I0 and I0", which connect to the negative pole. Rigidly mounted on connectors I'Il and I 0' is a copper cathoden connector bar Il. The cathode connector bar I I extends substantially the length of the cell and carries the cathode I3 bolted by means of'countersunk bolts I2 or otherwise suitably alxed to it. Since this connector presents no corrosion problem, a welded union is not necessary. Preferably a pair of bolted copper anode connector bars I4 and Ill fixed to connectors 9 and 9 are bolted by means of steel bolts I5 to an ironk or steel anode-supporting bar I6. This anode-supporting` bar supports pure electrodeposited nickel anodeA plates I?, I1 and I 'I" by means of bead welds I3 and I8' extending the` length of the top and bottom edges of the bar, applied using either a steel or, preferably, a nickel weld rod.

The superior corrosion resistance of copper under the conditions prevailing in the cell is ref-` sponsible for the durability of connectors 9 and 9. If a metal such as iron or nickel is employed for these connectors, it isY usually desirable to provide protective sleeves of copper or Monel;

While both connectors IU and I' may be con-y nected to the current source, this is normally'not necessary since theresistance of the copper bar II is too small to materially affect the operation. of the cell.

The nickel anodes of the cell illustrated in Figures 1 and 2 are composed of three separate cathodic nickel plates to secure the desired largey surface area. One or more plates may be used in this manner depending upon the size of plates available and the size of anode desired.

With particular reference to Figures 3 and 4, a plate nickel anode 2I composed of a single sheet of electrodeposited nickel is welded to a pair of square supporting bars 22 and 23 by bead welds 24, 24', 25 and 25. Cuifs or sleeves 26 and 21,

. composed of copper or a copper nickel alloy, may

be provided when the supporting bars are composed of another metal, to prevent corrosion of the supporting bar. While this construction is not essential, copper and its alloys have been nickel in resisting the corrosive action of the agents present in the cell electrolyte so that the life of the structure can be prolonged in this manner. The sleeves may be provided to cover only lthe immersed section of the bar above the anode or may extend up to the top of the cell.

The bars 22 and 23 may becylindrical rods with a side cutaway to providers, at face adjacent the anode, or they may be rectangular, hexagonal, or octagon'al bar stock, which can be turned down, ifv desired, to provide a cylindrical form where thel bar passes through the top of the cell, as shown in the drawing.

The electrolytic cell illustrated is designed for operationV with` an electrolyte level above the top of the anode and cathodev so that electrolyte can circulate freely around. the electrodes. The liquid level should be maintained above the bottom of barrier I so that hydrogen and uorne generated uvam u,... v

Ving a heating fluid through jacket 2;

faced-145 cannot r'nix in the gas space above the electrolyte.-

Forproduction o1 fiuorine thfcell is filled to a level slightly below operatinglevel -with an anhydrous electrolyte comprising van Iacid potassium \Product`gases are rwithdrawn continuously for purication or for use directly.

The application of the thermo-Siphon principleto the operation of electrolytic Icells as described herein is not claimed as our invention but constitutes the subject of U. S. Patent Application Serial Number 558,700 filed October 14, 1944.

It will be understood that we intend to include variations and modications of the invention and that the preceding examples are illustrations only and in no Wise to be construed as limitations upon the invention, the scope of which is dened in the appended claim, wherein We claim: 2

In an electrolytic cell for the generation of uorine comprising a single vertical plate type cathode and Ian anode comprising a nickel plate attached to a single surface of an anode support,

said anode support comprising a. substantially horizontal iron bar extending substantially completely across one face of said anode and welded to theinickel anode by substantially continuous welds along the horizontal edges of the bar near the top of the anode and on the side of the anode remote from the cathode, and a copper electrical connector comprising la vertical copper rod extending up through the top of the cell, and united to ia horizontal copper bar bolted to the iron anode-supporting bar.

ANTHONY F. BENNING. ROBERT C. MCHARNESS. MELBOURNE K. RICHARDS. GEORGE W. FELDMANN.

REFERENCES CITED y The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain June 4, 1935 

